Apparatus and method for expanding a stimulation lead body in situ

ABSTRACT

An implantable lead is provided with at least one extendable member to position therapy delivery elements, which may be electrodes or drug delivery ports, after the lead has been inserted into the body. The lead may formed as a resilient element which is contained in a retainer tube that may be removed to permit the lead to deploy. Alternatively, a non-resilient lead may be provided with a slotted retainer tube. A series of mechanical linkages for expanding and retracting the lead within the human body may be actuated with various mechanisms. A control system may be provided for closed-loop feedback control of the position of the extendable members. The invention also includes a method for expanding an implantable lead in situ.

RELATED APPLICATION

This is a divisional application of U.S. Ser. No. 09/862,104 filed May21, 2001, now U.S. Pat. No. 6,442,435 which is a continuation ofapplication Ser. No. 09/584,572 filed May 31, 2000, now U.S. Pat. No.6,292,702, which is a divisional of U.S. Ser. No. 09/070,136 filed Apr.30, 1998, now U.S. Pat. No. 6,161,047 for which priority is claimed.

BACKGROUND OF THE INVENTION

This invention relates to implantable leads for delivering therapy, inthe form of electrical stimulation or drugs, to the human body.Specifically, this invention relates to implantable leads that may beexpanded, retracted or adjusted after implantation in the human body.This invention also relates to mechanisms for accomplishing suchexpansion, retraction or adjustment of such leads in situ. Further, thisinvention relates to control systems, for controlling such expansion,retraction or adjustment of such an implanted lead.

Recent efforts in the medical field have focused on the delivery oftherapy in the form of electrical stimulation or drugs to preciselocations within the human body. Therapy originates from an implantedsource device, which may be an electrical pulse generator, in the caseof electrical therapy, or a drug pump, in the case of drug therapy.Therapy is applied through one or more implanted leads that communicatewith the source device and include one or more therapy delivery sitesfor delivering therapy to precise locations within the body. In drugtherapy systems, delivery sites take the form of one or more catheters.In electrical therapy systems, they take the form of one or moreelectrodes wired to the source device. In Spinal Cord Simulation (SCS)techniques, for example, electrical stimulation is provided to preciselocations near the human spinal cord through a lead that is usuallydeployed in the epidural space of the spinal cord. Such techniques haveproven effective in treating or managing disease and acute and chronicpain conditions.

Percutaneous leads are small diameter leads that may be inserted intothe human body, usually by passing through a Tuohy (non-coring) needlewhich includes a central lumen through which the lead is guided.Percutaneous leads are advantageous because they may be inserted intothe body with a minimum of trauma to surrounding tissue. On the otherhand, the types of lead structure, including the electrodes ordrug-delivery catheters, that may be incorporated into percutaneousleads is limited because the lead diameter or cross-section must besmall enough to permit the lead to pass through the Tuohy needle.

Recently, the use of “paddle” leads, like Model 3586 Resume® Lead orModel 3982 SymMix® Lead of Medtronic, Inc., which offer improved therapycontrol over percutaneous leads, have become popular among clinicians.Paddle leads include a generally two-dimensional set of electrodes onone side for providing electrical therapy to excitable tissue of thebody. Through selective programmed polarity (i.e., negative cathode,positive anode or off) of particular electrodes, electric current can be“steered” toward or away from particular tissue within the spinal cordor other body areas. Such techniques are described by Holsheimer andStruijk, Stereotact Funct Neurosurg, vol. 56, 199: pp 234-249;Holsheimer and Wesselink, Neurosurgery, vol. 41, 1997: pp 654-660; andHolsheimer, Neurosurgery, vol. 40, 1997: pp 990-999, the subject matterof which is incorporated herein by reference. This feature permitsadjustment of the recruitment areas after the lead has been positionedin the body and therefore provides a level of adjustment for non-perfectlead placement. Such techniques are disclosed in U.S. Pat. Nos.5,643,330, 5,058,584 and 5,417,719, the subject matter of which isincorporated herein by reference. Additionally, the value of atransverse tripole group of electrodes has been demonstrated for spinalcord stimulation, as described by Struijk and Holsheimer, Med & BiolEngng & Comput, July, 1996: pp 273-276; Holsheimer, Neurosurgery, vol.40, 1997: pp 990-999; Holsheimer et al., Neurosurgery, vol. 20, 1998.This approach allows shielding of lateral nervous tissue with anodes,like the dorsal roots, and steering of fields in the middle under acentral cathode by use of two simultaneous electrical pulses ofdifferent amplitudes.

One disadvantage recognized in known paddle leads is that theirinstallation, repositioning and removal necessitates laminectomies,which are major back surgeries involving removal of part of thevertebral bone. Laminectomies are required because paddle leads have arelatively large transverse extent compared to percutaneous leads. Thus,implantation, repositioning and removal require a rather large passagethrough the vertebral bone.

Another disadvantage with paddle leads is that optimal positioning isoften difficult during implant. For example, the transverse tripoleleads described above work optimally if the central cathode ispositioned coincident with the physiological midline of the spinal cord.Such placement is difficult since the doctor cannot see the spinal cordthru the dura during implant. Moreover, lead shifting may occursubsequent to implant, thereby affecting the efficacy of the therapydelivered from the lead.

Yet another disadvantage recognized with paddle leads is that the leadposition may change merely with patient movement. For example, when apatient lies down, the spacing between an epidural lead and the spinalcord decreases to a large extent, so that it is often necessary to lowerthe amplitude of the stimulation by half. It is reasonable to assumethat steering effects of a tripole lead might also be affected if theCSF width changes dramatically, or if due to patient twisting oractivity, the orientation between the lead and spinal cord changes.

While the prior art has attempted to provide deformable leads, which mayprovide improved insertion characteristics or enhanced stability onceinside the body, they have not succeeded in providing a device whichremedies the aforementioned problems. For example, U.S. Pat. No.4,285,347 to Hess discloses an implantable electrode lead having adistal end portion with a laterally extending stabilizer, preferably inthe form of curved loops. Similarly, and U.S. Pat. No. 4,519,403 toDickhudt discloses an inflatable lead for enhanced contact of theelectrode with the dura of the spinal cord. U.S. Pat. No. 5,121,754 toMullett discloses a device to allow electrodes to move to more lateralpositions after insertion, when a stiffening guidewire used duringinsertion is removed. In Mullett's device, only one electrode can befound at any particular longitudinal location, since only gentle curvesof the lead were designed, and the curves are not adjustable afterimplant of the lead. Similar problems apply to the device disclosed byO'Neill in U.S. Pat. No. 4,154,247.

Patent Cooperation Treaty (PCT) Publication No. WO 93/04734 to Galleydiscloses a lead tip that has four spans that will bulge into fourdifferent directions when a confining outer catheter is drawn proximallyback over the lead body. The publication describes one electrode on themiddle of each span. In situ in the epidural space, these fourelectrodes will form a square or rectangular cross-sectional shape. Twoof them might be pressed into the dura (at lateral positions) and theother two would be dorsal, against the vertebral bone. Only theelectrodes nearest the spinal cord would be useful for programming.While this could give two electrodes at the same longitudinal position,their medial to lateral locations are difficult to control, and theirability to spread apart depends on the relative stresses in the spansand tissue-like adhesions that may be present. Other malecot-type leadtips have been proposed for positioning of electrodes in the heart (U.S.Pat. No. 4,699,147, Chilson and Smith, 1985; U.S. Pat. No. 5,010,894,Edhag, 1989) or anchoring of lead bodies (U.S. Pat. No. 4,419,819,Dickhudt and Paulson, 1982; U.S. Pat. No. 5,344,439, Otten, 1992) orpositioning of ablation electrodes (Desai, U.S. Pat. Nos. 5,215,103,5,397,339 and 5,365,926). While the aforementioned prior art devicesprovide various configurations for compact insertion or leadstabilization after implant, they do not offer the advantages andimproved efficacy recognized with respect to paddle lead configurations.

It would therefore be desirable to provide a lead structure forstimulation of excitable tissue surfaces which combines the advantagesoffered by percutaneous leads with respect to minimized trauma duringinsertion, repositioning and removal with the advantages offered bypaddle-type leads with respect to improved efficacy, ability to provideelectrodes in places lateral to the axis of the lead and tailoring oftreatment.

It would also be desirable to provide a lead structure which permitsadjustment of the lead dimensions and therefore the delivery sitelocation in situ for enhanced control of the therapy being applied tothe excitable body tissues.

It would be further desirable to provide a paddle lead which is capableof automatically adjusting its width or delivery site spacingautomatically in response to patient factors such as body position oractivity or in response to a parameter such as muscle contraction oraction potentials, which may be characteristic of the stimulation ortherapy being applied.

SUMMARY OF THE INVENTION

The invention combines the advantages of percutaneous leads with thoseof paddle leads. In a preferred embodiment, the invention provides alead structure including a central core portion and at least oneflexible, semi-flexible or semi-rigid transversely extending span whichmay be positioned in a compact position during insertion in which it iswound around or otherwise disposed in close proximity to the centralcore portion. Each span may also be deployed or shifted to a position inwhich it extends outward from the central core portion in a transversedirection. Each span has disposed on one surface a number of therapydelivery elements, in the form of electrodes or catheter ports, fordelivering therapy in the respective form of electrical or drug therapyto the body. In the compact insertion position, the lead may be easilyinserted within a catheter or Tuohy needle. Once the lead has beenpositioned at the appropriate place in the body, the span or spans maybe deployed from the compact position to the extended position in whichthe therapy delivery elements are positioned in a fashion similar to apaddle lead. The flexibility of the spans also permits the lead to beretracted back to the compact position in the event that the lead mustbe removed from the body.

In a preferred embodiment, the invention provides a lead which includesa central core portion and at least one flexible paddle extendingtherefrom and which may be coiled around the core portion when the leadis to be compacted for insertion. As the lead is inserted through acatheter or Tuohy needle, the spans are kept in the compact position bylead rotation in a direction opposite their direction of winding aroundthe central core. Also according to the invention, the spans aredeployed by rotating the central core portion in the same direction inwhich the spans are coiled around the central core portion. Because ofthe flexibility of the spans, they are caused to move outward, away fromthe central core as the lead is uncoiled. In another embodiment of theinvention, the spans can be formed of a resilient material in which toresilient forces develop when the lead is configured in its compactposition. The lead is maintained in its compacted form while inside ofthe insertion tool, i.e. Tuohy needle. The resilient forces cause thespans to extend outward once the lead exits the end of the insertiontool.

An outer concentric retainer tube may be provided in combination withthe lead, the outer retainer tube acting to retain the lead in itscompact position during insertion. The retainer tube may be providedwith a pair of notches on its distal end to aid in the retraction of thelead after deployment. Specifically, the notches are disposed on thedistal end of the retainer tube in such a manner that the spans willengage the notches when the central core portion is rotated and pulledtoward a proximal end of the retainer tube. The notches retain the spansin position as the central core rotates, thus causing the spans to coilaround the central core portion and assume a compact position.

The present invention also provides a lead which may be compacted in adifferent manner than described above. The lead is comprised of a seriesof therapy delivery elements which are attached to a thin backing sheetwhich permits the sheets to be disposed one on top of the other in thecompact insertion position and then to expand to a generally planarorientation once the lead is inserted to the appropriate position in thebody.

The following are exemplary advantages of adjustable leads constructedaccording to the preferred embodiments of the invention:

1. The spacing of the sites can be matched to important dimensions ofthe tissue affected, e.g., the width of the Cerebro-Spinal Fluid (CSF)between the dura and the spinal cord.

2. As the dimensions of the lead tip are changed, the locations of thesites relative to the tissue affected may be advantageously altered. Forexample, as a paddle's width is increased the paddle will move towardthe spinal cord in the semicircular dorsal part of the epidural space.

3. In cases where the bones or fluid compartments have large widths(e.g., CSF depth at spinal level T7 or T8) or are too wide in aparticular patient, the paddle width can be increased appropriately toensure effective therapy.

4. Changes in paddle width and the accompanying medial and lateralmovement of the sites can have a beneficial effect on the therapy. Forexample, the ability to stimulate only the medial dorsal columns versusthe more lateral dorsal roots may provide enhanced therapeutic results.

5. As the patient ages, their pathological condition changes, theirdegree of fibrosis or scar tissue changes, or the effects of the therapychange, adjustments of the paddle dimension(s) might restore or maintainthe benefit.

6. If the paddle's dimension(s) can be changed after implant, it may bepossible it) optimize the benefits and minimize undesirable sideeffects.

7. By changing the paddle's dimension(s), it may be possible to avoidsurgery to replace or reposition the lead.

8. By changing the paddle's dimension(s), it may be possible to positionthe sites optimally relative to important physiological locations, e.g.,the physiological midline of nervous tissue, or receptors responsive tothe drugs being delivered.

9. It may be possible to minimize the use of energy by optimizingefficiency of therapy delivery through adjustment of paddle width.

10. There may be minimal insertion trauma and operating room time andresources needed if it is possible to place a lead with percutaneoustechniques, and then expand it in situ.

11. Repositioning of a paddle lead can be done without laminectomy.Removal is also made quicker and less traumatic.

12. With closed loop feedback control of the paddle's dimension(s),optimal therapy can be maintained with less interference with thepatient's lifestyle.

Another preferred embodiment allows automatic changes in at least onedimension of a paddle lead. Such a system would measure an effect of thestimulation, e.g., a compound action potential caused bystimulation/drugs, a muscle contraction, the direction of gravity,increased activity of the patient, relative motion of vertebral bones,or other effects. Measurement techniques for compound action potentialsare disclosed in U.S. Pat. No. 5,702,429 the subject matter of which isincorporated herein by reference. Such a recorded signal should bealtered if the lead paddle dimension that is controlled is changed.Then, after filtering, amplifying, integrating and comparing therecorded signal to a previous stored signal, the parts of the lead thatcontrol the dimension in question will be moved or activated, causing achange in said dimension, which will restore the effect measured to itsoriginal value. This constitutes closed loop feedback control, and canenable to patient to be less affected by changes in the therapy causedby his/her position, activity, etc. Of course there should be governorson the dimensional changes allowed, so that if the measured parameter isvery greatly changed, neither the device nor the patient will undergodamage or trauma. The described embodiments show preferred techniques toexpand a lead in directions transverse to the main axis of the leadbody. The invention also contemplates devices for expanding the lead ina direction substantially parallel to the lead axis.

Other advantages novel features, and the further scope of applicabilityof the present invention will be set forth in the detailed descriptionto follow, taken in conjunction with the accompanying drawings, and inpart will become apparent to those skilled in the art upon examinationof the following, or may be learned by practice of the invention. Theadvantages of the invention may be realized and attained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which are incorporated into and form a part ofthe specification, illustrate several embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings, in which likenumbers refer to like parts throughout:

FIG. 1 is a plan view of a lead according to the present invention beinginserted through a Tuohy needle near the dura of a human spine;

FIGS. 2A-2D are isometric views of a lead according to the presentinvention in a compact insertion position;

FIG. 2E is an isometric view of the lead of FIG. 2A in an expanded ordeployed position;

FIG. 3 is an isometric view of a lead according to another embodiment ofthe invention;

FIG. 4A is an isometric view of a lead and retainer tube according toyet another embodiment of the invention;

FIG. 4B is an isometric view of a lead retainer tube according to thepresent invention;

FIG. 4C is an isometric view of a lead and retainer tube according tothe present invention;

FIG. 5A is an isometric view of a lead and expansion mechanism accordingto another embodiment of the present invention;

FIG. 5B is a top view of the lead of FIG. 5A in a compact position;

FIG. 6A is a cross section of a lead according to another embodiment ofthe invention;

FIG. 6B is a front view of an expansion mechanism according to apreferred embodiment of the present invention;

FIG. 7 is a front view of an expansion mechanism according to anotherpreferred embodiment of the present invention;

FIGS. 8A and 8B are front views of an expandable lead according toanother preferred embodiment of the invention;

FIG. 8C is a front view of the expandable lead of FIGS. 8A and 8B withan alternative embodiment for the actuating mechanism;

FIGS. 9A and 9B are side and front views, respectively, of anotherpreferred embodiment of the present invention;

FIGS. 10A and 10B are front views of another preferred embodiment of thepresent invention;

FIGS. 11A and 11B depict yet another preferred embodiment of the presentinvention;

FIG. 12A is a front view of an adjustment mechansim according to apreferred embodiment of the invention;

FIG. 12B is a front view of an adjustment mechansism according toanother preferred embodiment of the invention;

FIG. 12C is a front view of an adjustment mechansim according to yetanother preferred embodiment of the invention; and

FIG. 12D is a front view of an adjustment mechansim according to stillanother preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a lead according to a preferred embodiment of theinvention being utilized in an SCS implementation. In accordance withknown techniques, a Tuohy needle 14 is positioned near the dura 12 ofspine 10. Lead body 20 is inserted through the lumen of Tuohy needle 14and positioned near the dura 12. A proximal end (not shown) of lead body20 is connected to a source device (not shown) which may be a pulsegenerator, in the case of electrical stimulation, or a drug pump in thecase of drug therapy. Although the invention will be described hereinwith reference to SCS procedures and the embodiments described inrelation to electrical therapy, it will be recognized that the inventionfinds utility in applications other than SCS procedures, including otherapplications such as Peripheral Nervous System (PNS) Stimulation, SacralRoot Stimulation, Cortical Surface Stimulation or Intravecular CerebralStimulation. In addition, the invention finds applicability to SCSprocedures where the lead is placed in the intrathecal (subdural) space.The invention also finds utility to drug therapy where electricalcomponents are replaced with conduits and catheters for conducting drugmaterial to the therapy site. In this case, especially, the lead may beplaced in the intrathecal space.

FIGS. 2A thru 2D illustrate a lead according to a preferred embodimentof the present invention. Lead 20 is provided with a distal tip 30 thatmay be compacted for insertion and unfolded after it has been positionedappropriately within the body. Distal tip 30 includes a central portion32 which has at least one span 34 depending therefrom. Span 34 iscomprised of a flexible, insulative material, such as polyurethane orsilicone rubber. The term “flexible” as used herein refers to bothresilient and non-resilient materials. Central portion 32 may have agenerally semi-circular cross-section as shown, or may be flat. Acentral passage 33 may run axially along the inside of lead 20. Acentering stylet 25 is provided through central passage 33 and extendsin a distal direction through central portion 32 for engaging a part ofthe body, such as adhesions in the epidural space, to stabilize lead tip30 as it is deployed. Affixed to a surface of spans 34 and to thecentral portion 32 is a series of other therapy delivery elements in theform of electrodes 36A-E. In accordance with the invention, lead 20 maybe configured into a compact insertion position shown in FIG. 2A. Asshown in FIG. 2B, spans 34 are coiled around central portion 32 suchthat the lateral extent of lead tip 30 is no larger than the lumen ofTuohy needle 14.

Once in position within the epidural space, lead tip 30 may be deployedout of the Tuohy needle 14, as shown in FIG. 2C. FIG. 2D shows the viewfrom the side opposite the side illustrated in FIG. 2C. In theembodiment described in which the spans are flaccid or semirigid,deployment of lead tip 30 may be implemented by rotating the lead body20 in a counterclockwise direction once lead tip 30 is beyond the end ofthe Tuohy needle in a desired position. As spans 34 encounter dura ordorsal bone of spinal canal, they can uncoil to assume a generallyplanar shape in which electrodes 36A-E are disposed on one side of thelead facing the dura, as shown in FIG. 2E. As shown in phantom in FIG.2D, electrodes 36A-E communicate electrically with the source device(not shown) via conductor paths 39 and 41. Conductor paths 39 and 41 maybe comprised of a flexible electrical conductor or thin wires which areembedded or molded within lead 20.

In the case of drug therapy, the electrodes 36A-E illustrated in FIGS.2C-E would be replaced by ports which act as therapy delivery elementsto convey drug to the body. Similarly, conductor paths 39 and 41 wouldbe replaced by conduits formed in the interior of lead 20 for conveyingdrug from the source device. Stylet 25 may be left permanently in theepidural space or may be withdrawn from the lead 20 after the lead tip30 is uncoiled. In the case of a drug delivery device, stylet 25 mightremain as a catheter at some preferred distance.

FIG. 3 illustrates another embodiment of the invention in which lead 20is provided with a pair of guide pins 40 which are affixed to a moreproximal removable sheath 41 that surrounds lead body 20. Alternatively,guide pins may be formed integrally on Tuohy needle (not shown). Guidepins 40 act to guide spans 34 outward as the lead body 20 is rotated ina counterclockwise and to guide spans 34 to coil around central portionas lead body 20 is rotated in a clockwise direction. Guide pins 40 maybe comprised of a rigid, material and may be extended or retracted fromsheath 41 or Tuohy needle 14. After spans 34 are deployed, sheath 41 maybe removed.

FIG. 4A illustrates another embodiment of the invention in which spans34 are formed as resilient or elastic elements. The term “resilient” asused herein refers a tendency to return to an undeformed state oncespans 34 are no longer compressed to lay beside central part 32. Inaccordance with this embodiment of the invention, a retainer tube 50 isprovided to retain lead tip 30 in its compacted position untildeployment is desired. Retainer tube 50 includes an inner passage whichis sufficient to accommodate the diameter or lateral extent of lead body20 and its compact shape-changing tip 30. The outer diameter of retainertube 50 is small enough that retainer tube 50 may also be insertedthrough the lumen of Tuohy needle 14 (FIG. 1). Alternatively, tube 50may replace the Tuohy needle. Spans 34 are formed in such a manner thatthey have a tendency to undertake a position in which they are extendedfrom central portion 32. Thus, in the compact insertion positionillustrated in FIG. 4A, resilient forces are present in spans 34 to urgethem outward into their extended, uncoiled position. The resiliency ofspans 34 may derive from the polymeric material used to construct spans34 or from resilient elements like wires (not shown) which areincorporated into the interior or onto the exterior surface of spans 34.

Referring to FIGS. 4B and 4C, in accordance with yet another preferredembodiment of the invention, a notch 60 is provided in a distal end 52of retainer tube, 50 to facilitate retraction of a deployed lead.Preferably, one notch is provided for each span 34 provided on lead tip30. In operation, retainer tube 50 is inserted around a proximal end(not shown) of lead body 20 and pushed towards lead tip 30 a sufficientdistance until retainer tube 50 encounters lead tip 30. Lead body 20 isthen pulled in a proximal direction and simultaneously rotated, in adirection which may be clockwise or counterclockwise, until lower edges37 of spans 34 slide into notches 60. Under continued rotation of leadtip 30 and lead 20, notches 60 function to guide spans 34 into theircoiled, compacted position. Once compacted, lead 20 may be retractedfurther into retainer tube 50. Compacted lead 20 and retainer tube 50may then be repositioned to a higher or lower point along the spinalcord or may be removed from the body.

FIGS. 5A and 5B illustrate an expandable lead tip 130 according toanother embodiment of the invention. Referring to FIG. 5B, lead tip 130is comprised of a series of electrodes 136A-E which are fastened to aflexible insulative backing sheet or span 140. The central portion oflead tip 130 is comprised of middle electrode 136C. Span 140 may beconstructed of polyurethane or DACRON-reinforced silicone rubber.Electrodes 136A-E are in electrical communication with source device(not shown) via a series of conductors 139 incorporated into or ontospan 140. Electrodes 136A-E are embedded in span 140 or fastened byadhesive or other known means. Ends 142 of span 140 are provided witheyelets 144 for fastening to an expanding mechanism which will bedescribed below. This aspect of the invention provides a lead tip 130which may assume a compacted position, in which electrodes 136A-E arestacked one on top of the other such that the thickness of lead tip 130may be reduced to a dimension that is slightly larger than thecollective thicknesses of electrodes 136A-E.

Referring to FIG. 5A, lead tip 130 may be expanded with the use of anexpansion mechanism 150 according to one aspect of the invention.Expansion mechanism 150 comprises a series of struts 152 which arepivotally linked to one another such that points A and B may be causedto move towards and away from one another in order to compact or expandlead tip 130, respectively. A first linkage 156 is pivotally connectedto struts 152A and 152B. A second link 158 is pivotally connected tolinks 152C and 152D. First and second links 156 and 158 extend to aproximal end of lead body 20 where they can be individually actuated bya clinician. By moving first link 156 with respect to second link 158,points A and B are caused to move toward or away from one another,thereby contracting or expanding lead tip 130. By using rigid struts andlinkages, sufficient farces can be applied so that a space may becreated for the expanded size of lead tip 130. Introductory Sheath 170may be removed after lead tip 30 is expanded. Or, as another embodiment,it might remain in the position shown, and a locking mechanism to keeplinks 156 & 158 at a constant position might be able to compress sheath170 over the two links. A tether 180 sets a limit on the separation ofpoints A and B, and guarantees that electrodes are evenly spaced whenthe length of tether 180 equals the length of span 140.

FIGS. 6A and 6B illustrate another embodiment of the invention. FIG. 6Ais a cross-section of a lead tip 230 according to a preferred embodimentof the invention which comprises a single span 234 incorporating aseries of conductors 236A-F therein. FIG. 6B illustrates a plan view ofa mechanism 250 suitable for deploying lead tip 230 or a stack ofelectrodes as shown in FIG. 5B. Mechanism 250 comprises a pair of links252A and 252B pivotally connected to one another and each pivotallyconnected to a respective actuator link 258A and 258B. Through relativemovement of actuator links 258A and 258B, point A is caused to movetoward or away from link 258A, thereby causing contraction or expansionof lead tip 230 or 130. One eyelet 144 on span 234 is attached to pointA, and the other eyelet may slide on link 258A. With this embodiment,since the lead tip is pulled in one direction, mechanism 250 in itsinitial, collapsed position, should be positioned toward one side, forexample, over the dorsal roots on one side of the spinal cord. In theexpanded position, point A would advance to the opposite dorsal roots.Once again, a way to lock point A at a certain expanded position is tohave an anchor along sheath 170 that compresses and holds sheath 170against links 258A and 258B. Like mechanism 150, by using rigid strutsand linkages, a space can be created for lead tip 230.

FIG. 7 illustrates an expansion mechanism according to another preferredembodiment of the invention. Lead tip 130 may be expanded with the useof mechanism 350, comprised of struts 311 and 310. Linkage 330 ispivotally connected to the end of these struts. Linkage 340 is pivotallyconnected to the center of these struts. As linkages 330 and 340 aremoved relative to each other be a clinician, tips 360 will move togetheror apart. Eyelets 144 of lead tip 130 (FIG. 5B) can be connected to tips360.

FIGS. 8A and 8B illustrate an expandable lead according to anotherpreferred embodiment of the present invention. The lead comprises aflexible outer coaxial accessory tube 802 which is mounted over thedistal end of lead body 801. A stop 806 is affixed to the distal end oflead body 801 to prevent movement of the upper end 830 of accessory tube802 relative to lead body 801. The lower end 832 of accessory tube 802is adapted to slide with respect to lead body 801. Accessory tube 802includes a central slot 805 forming two flexible leaf portions 820 and822. A recess 824 is provided in each leaf portion 820 to form a bendingjoint therein. The lower end 832 may be moved upward, thereby causingleaf portions 820 to bend and deploy outward from the lead body 801. Toaccuate the mechanism an actuator 807 is slid over the axial tube 801 bythe clinician. While holding onto the axial tube 801, the clinicianpushes the actuator 807 against the accessory tube which causes the slot805 to separate and the lead to open as illustrated in FIG. 8B. A seriesof ratchet rings 811, 812 and 813 are formed in lead body 801 to preventdownward movement of lower end 832 of accessory tube 802 to therebyretain the leaf portions 820 in their outward, deployed position. Theserachet rings will also allow and hold different amounts of lateralexpansion to be chosen by the clinician. A rigid barrel electrode 803 ismounted on each leaf portion 820 of the accessory tube 802. In theexpanded position of accessory tube 802, central electrodes 808, 809 and810 are exposed. Central electrodes 808, 809 and 810 and barrelelectrodes 803 communicate electrically with the source device (notshown) through electrical conductors (not shown) within the lead body.

FIG. 8C illustrates an expandable lead according to another preferredembodiment of the present invention. This embodiment is the same as thatillustrated in FIGS. 8A and 8B except that a screw actuator is providedfor precise adjustment of the outward deployment of leaf portions 820.The axial lead body 801 has a threaded portion 811 formed therein. Athreaded drive nut 812 is mounted on the threaded portion of the leadbody 811. The drive nut has multiple indented holes 812 a to receive anactuation driver similar to 813. The drive nut is interlocked by pins(813 a) on an actuation driver 813 and rotated by the driver. This screwapparatus allows finer adjustment of the expansion and also adjustmentof the expansion after implantation of the lead device.

FIGS. 9A and 9B illustrate another embodiment of the invention.Mechanism 450 can have a central element 410 that may contain anelectrode or catheter port 405. It may house progressively smallermobile telescoping parts 420, 430, 440 that can be pushed outward towardone or more directions. Each mobile part is provided with a shoulder 422to limit its outward movement and to recruit an adjacent mobile part. Atab 424 is provided to limit inward movement. For an expansion in oneplane, element 410 may have inside it one or more mechanisms 150 (FIG.5A), 250 (FIG. 6B) or 350 (FIG. 7). Alternatively, there might besingle, curved linkage passing along lead 20 and attached to the finalelectrode or catheter port site 445. As this linkage is moved by aclinician, site 445 will move outward or inward, and itermediate siteswill follow if the movement of each site relative to the next site islimited.

FIGS. 10A and 10B illustrate another embodiment of the invention. InFIG. 10A, the lead 20 is in a compacted position, with elastic andresilient transverse spans 500 bent to remain inside the lumen of Tuohyneedle 14. Spans 500 are adapted to bend to a position substantiallyparallel to the axis of lead 20 in the compact position. Once the leadis pushed beyond the needle, spans 500 will move by their resiliency totheir natural position, as shown in FIG. 10B. Those of ordinary skillwill note that the grouping of central electrode or catheter port 510and the two nearest side electrodes or ports 520 form a tripole/triportarrangement transverse to the longitudinal direction of the lead 20. Theclinician may have to place and manipulate a mechanism like 150, 250 or350 prior to placement of this lead to create a space. Alternatively, ametal material like NITINOL may be placed inside span 500 and treated sothat its position after removal of the confinement of needle 14 will beperpendicular to the lead axis.

FIGS. 11A and 11B illustrate another embodiment of the invention. InFIG. 11A, the lead 20 is in a compacted position with elastic andresilient spans 600 bent to remain inside the lumen of Tuohy needle 14.There is a central electrode or catheter port 610. The lateralelectrodes/ports 620 are on members that will remain parallel to thelead axis due to pivot points 630 and equal length spans 600 above andbelow.

In FIG. 11B, the lead tip is beyond the introducing needle. The spans600 resume their normal, unstressed positions perpendicular to the leadbody axis. Lateral electrodes/ports 620 are on either side of centralelectrode/port 610. Removal may be accomplished by pulling on the leadbody with sufficient force to bend the spans 600 back along the leadbody, or by pushing another catheter or needle over lead 20. It isrecommended that there be a thin, inert and flexible film (not shown)over the space between spans to help removal by preventing tissueingrowth. One embodiment of the invention is to lock linkages as shownin FIGS. 5-7 into a fixed orientation by using a compressive sleeve tosqueeze the lead body 20 inward against the linkages. This sleeve may bean anchor to superficial (subcutaneous) tissue. To make a change, minorsurgery can be done to cut down to this anchor, loosen or remove it,adjust the positions of the linkages, replace the anchor/compressivesleeve, and resuture the wound. Obviously, the clinician and patientneed to believe that the benefits of such a procedure out weigh thediscomfort and risks.

FIGS. 12A through 12D illustrate mechanisms that may be used to operatethe linkages illustrated and described with respect to FIGS. 5A, 6B, 7and 9 in accordance with preferred embodiments of the invention. FIG.12A illustrates an embodiment of the invention that allows chronicadjustment of the relative positions of two actuating members 710 and720. A rigid needle 775 with a sharp hexagonal tip 785 is passed throughthe skin and engages a hexagonal receptacle (possibly via reductiongears) 790 that is capable of turning a circular component 760 inside ofa container 750 beneath the patient skin. On end of this container 750attaches to the lead body 20, which contains the two actuating members710 and 720 and wires/catheters 730 that go to the distal tip of thelead 20. Another end of the container 750 connects to a lead 721 thatconveys the wires/catheters 730 to a source device (not shown).Actuating members 710 and 720 are connected to the rotating component760 are connected to the rotating component 760 by pivot points 770 and780. As the needle 775 is rotated, the linkages 710 and 720 will moverelative to each other. This device 750 should be large enough to bepalpated under the skin, and the rotating component 760 should be largeenough so that limited rotation of approximately 60° causes sufficientmovement of the linkages.

FIG. 12B illustrates another preferred embodiment of a linkage actuatingmechanism according to a preferred embodiment of the invention. Thisembodiment allows chronic adjustment of the position of one linkage 810relative to the lead body 20 using a rack gear and pinion geararrangement. This embodiment may be used with a two-actuating memberconfiguration as described with respect to FIG. 12A, where one actuatingmember is fixed with respect to lead body 20. As in the embodimentdescribed above with respect to FIG. 12A, a rigid needle (not shown)with a hex-head sharp tip is passed through the patient's skin andengages a hexagonal receptacle 865 that drives an internal gear 860 ofsubcutaneous container 850. As gear 860 turns possibly with the aid ofreducing gears, it will move the actuating member 810 back or forth,which has gear teeth 840 formed on its proximal end. A stop 870 preventsexcessive movement of actuating member 810. A wire/catheter group 830passes from lead 20 through the container to another lead 821 from thesource device. Alternatively, the source device could be on the backside of the container 850. It will be recognized by those of ordinaryskill that there could be a number of gears inside container 850 tochange the direction of movement of the actuating member 810, forexample, to a rotary direction.

FIG. 12C illustrates another preferred embodiment of a linkage actuatingmechanism according to a preferred embodiment of the invention. Thisembodiment allows chronic adjustment of the position of linkage 910relative to the lead body 20. Again, this embodiment may be used withtwo linkage configurations where on linkage is fixed with respect to thelead body 20. This embodiment utilizes a hydraulic cylinder arrangementto actuate linkage 910. In this case a noncoring hypodermic syringeneedle (not shown) is passed through the patient's skin and through acompressed rubber septum 960 provided on the side of container 950.Fluid may be added or withdrawn from beneath the septum, which isconnected to a syringe 940. The moveable plug of this syringe 920 isconnected to the moveable linkage 910. Again, the wires/catheters 930from the proximal tip of lead 20 pass through container 950 and on tothe source device. Alternatively, the source device could be on the backside of container 950, although, for drug delivery, there would need tobe another system on the front of container 950 for refilling the drug.

FIG. 12D illustrates an actuating mechansim according to a preferredembodiment of the present invention that allows chronic adjustment ofthe degree of rotation of linkage 1010 relative to lead body 20. A rigidneedle with a hex-head sharp tip can be inserted into a hexagonalreceptacle 1070 in container 1050. Rotation of this needle devicerotates gear 1020 which causes rotation of gear 1040 attached to linkage1010. There may be restrictions on the movement of gear 1020 to preventexcessive rotation.

The embodiments shown in FIGS. 12A-D demonstrate devices to actuatelinkages that pass to the distal tip of the lead and cause changes inone or more dimensions of the lead paddle. As described, these involvetransmission of force or energy through the skin by means of a needlethat passes through the skin. The same effects can be achieved by havinga small motor implanted into the container parts shown, or into thepower source itself (not shown) which runs on an electrical battery ortransmitted and received radio frequency signal, such as the motorprovided in the totally implantable, programmable drug device calledSynchroMed®, manufactured by Medtronic, Inc. of Minneapolis, Minn.Smaller motors may be acceptable, especially if a sequence of gears maybe used to provide mechanical advantage. If such motors are used, thereshould be a mechanical circuit breaker to prevent excess motion of thelinkages.

Very similar techniques would allow expansion of a lead in a directionparallel to the lead body. For example, telescoping elements withelectrodes could move parallel to the axis of the lead body (parallel tothe spinal cord), similar to the way a car antenna can be extended andretracted. By attaching electrodes and catheter ports to the axiallinkages of FIGS. 5 through 8, or attaching eyelets 144 of compactedgroups of electrodes/ports such as items 130 or 230, it is possible toextend or compact said groups of electrodes in an axial direction. Thisis a valuable feature if one wishes to match the axial spacing ofelectrodes/ports to important dimensions of the structure to bestimulated/affected. For example, Holsheimer (Neurosurgery, vol. 40,1997: pp 990-999) has shown that there may be preferred longitudinalspacing of electrodes based upon the recruitment factors in spinal cordtissue, and also critically dependent upon the width of the CSF(cerebrospinal fluid) layer between the spinal cord dorsal surface andthe dura mater. Therefore, we wish to include the ability to increase ordecrease the longitudinal spacing between electrodes/ports by theseinventions, and to be able to make a change in said spacing afterinitial implant of a complete therapeutic system.

Those skilled in the art will recognize that the preferred embodimentsmay be altered or amended without departing from the true spirit andscope of the invention, as defined in the accompanying claims.

What is claimed is:
 1. An implantable medical device comprising: atleast one implantable lead for providing delivery of therapy to a bodycomprising an elongate central portion having an axis, the implantablelead further comprising at least one extendable member having an end,the extendable member depending from the central portion and beingadapted to assume a range of positions, including a compact position, inwhich the end is disposed in close proximity to the central portion, andan extended position, in which the end is disposed at a location distalfrom the central portion, the implantable lead further comprising atleast one therapy delivery element disposed on the extendable member fordelivering therapy to the body, and means for position adjustment of theextendable member throughout the range of positions at any time in situafter surgical implant, wherein the means for position adjustment of theextendable member comprises an implantable motor operatively connectedto the extendable member to cause movement of the extendable member,wherein the means for position adjustment further comprises a linkageassembly comprising at least one actuating member operatively connectedto the implantable motor and the extendable member to cause movement ofthe extendable member with movement of the at least one actuatingmember.
 2. The implantable medical device of claim 1, wherein the atleast one actuating member moves in a direction substantially parallelto the axis of the central portion.
 3. The implantable medical device ofclaim 1, wherein the means for position adjustment further comprises arack gear and a pinion gear, the rack gear being operatively connectedto the at least one actuating member to cause movement of the extendablemember, wherein the implantable motor is operatively connected to therack gear to cause movement of the extendable member.
 4. The implantablemedical device of claim 2 wherein the means for position adjustmentfurther comprises a hydraulic cylinder, the hydraulic cylinder beingoperatively connected to the at least one actuating member to causemovement of the extendable member, wherein the implantable motor isoperatively connected to the hydraulic cylinder to cause movement of theextendable member.
 5. The implantable medical device of claim 1, whereinthe means for position adjustment further comprises a rotational shaftand gear mechanism operatively connected to the at least one actuatingmember to cause movement of the extendable member, wherein theimplantable motor is operatively connected to the rotational shaft andgear mechanism to cause movement of the extendable member.
 6. Theimplantable medical device of claim 1, wherein the extendable member isresilient.
 7. The implantable medical device of claim 1, wherein theextendable member is formed as a series of telescoping elements.
 8. Theimplantable medical device of claim 1, wherein the extendable member isformed as a series of telescoping elements.
 9. The implantable medicaldevice of claim 8, wherein the telescoping elements are provided withsaid at least one therapy delivery element thereon.
 10. The implantablemedical device of claim 1, further comprising an inert and flexible filmover a space between extendable members or between an extendable memberand the elongate central portion.
 11. The implantable medical device ofclaim 1, wherein the central portion has at least one part that rotatesand wherein the rotation of the at least one part of the central portionthat rotates results in a coiling or uncoiling of the extendable memberaround the central portion.
 12. The implantable medical device of claim1, wherein the extendable member incorporates a resilient material tourge the extendable member towards the extended position.
 13. Theimplantable medical device of claim 1, further comprising a centralpassage in the central portion for accommodating a centering stylet tostabilize and center the implantable lead.
 14. The implantable medicaldevice of claim 1, wherein the at least one therapy delivery elementcomprises two or more therapy delivery elements and wherein theextendable member is adapted to be folded in a manner that the therapydelivery elements are disposed one on top of the other in the compactposition.
 15. The implantable medical device of claim 1, wherein theextendable member comprises a transverse extendable member adapted tobend to a compact position in which the extendable member extends in adirection substantially parallel to the axis of the central portion andwherein the extendable member is adapted to extend in an extendedposition at an angle of 90 degrees or less to the axis of the centralportion.
 16. The implantable medical device of claim 1, wherein themeans for position adjustment further comprises a gear, the gear beingoperatively connected to the at least one actuating member to causemovement of the extendable member, wherein the implantable motor isoperatively connected to the gear to cause movement of the extendablemember.